Cast iron valve seat insert



Oct. 30, 1956 A. A. ARMSTRONG CAST IRON VALVE SEAT INSERT Filed Sept.16, 1953 411mmllllllll LL 40/144 4; A/MHI/QO/V IYV'ERZZUZT /ewwmmwwmm43/ United States Patent CAST IRON VALVE SEAT INSERT Adua A. Armstrong,Mentor, Ohio, assignor to Thompson Products, Inc., Cleveland, Ohio, acorporation of Ohio Application September 16, 1953, Serial No. 380,461

Claims. (Cl. 148-31) This invention relates to cast valve seat insertshaving high collapse resistance. Specifically, this invention deals witha heat-treated cast silicon-chromium steel engine valve seat insert.

It is known that when metal is heated to very high temperatures forextended periods of time, it will congeal or set in an expanded stateand willnot contract as usual when cooled. Since engine valve seatinserts are press-fitted in recesses in engine cylinder heads or blocks,when heated in operation of the engine, they expand to a point wherefurther expansion is restricted by the cylinder metal. At this point,continued expansion due to increased temperatures, will cause theinserts to bow inwardly or away from the restricting shoulder or wall ofthe engine head or block. Then, if the bowed inserts reach the settingtemperature and are cooled from this temperature, the cylinder metalshrinks away from the insert and the insert becomes loose in the engine.The bowed and setinserts are known as collapsed inserts and thetemperature at which they take the permanent set is known as thecollapse temperature.

Heretofore, valve seat inserts have been produced by expensive forging,machining, and heat-treating procedures. The best of these prior knowninserts had to be annealed, hardened, quenched, tempered, and drawn to aRockwell hardness of about 35 C. The microstructure of these prior knowninserts was generally an aggregate of carbides with some martensiteoriented in an interdendritic pattern and having some of the carbides inthe grain boundaries and scattered throughout the matrix. Thismicrostructure, however, did not provide collapse resistance attemperatures above about 800 F.

Since the modern, high-speed, high-compression internal combustionengines frequently operate at valve seat insert temperatures above 800F., loose-collapsed inserts have presented a seriou engine problem.

The present invention now provides inexpensive cast, heat-treated,silicon-chromium steel alloy valve seat inserts of unique microstructureand having a collapse temperature from 200 to 300 F. above the bestprior known valve seat insert produced by the more expensive prior knownforging and heat-treating techniques. Thus, the cast, heat-treatedinserts of this invention have a collapse temperature between about 1000to 1100 F. as compared with the maximum 800 F. collapse temperature offorged inserts. In addition, the hardness and wear resistance of thecast valve seat inserts of this invention are at least equal to orgreater than the best prior known inserts produced by the more expensiveforging and heat-treating processes.

Accordingly, it is an object of this invention to provide cast,heat-treated, silicon-chromium steel valve seat inserts having enhancedresistance to collapse.

Another object of the present invention is to provide a cast,silicon-chromium steel alloy for valve seat inserts having uniquemetallurgical properties.

A further object of this invention is to provide a "ice method of makingvalve seat inserts of increased collapse resistance.

A further object is to provide an inexpensive, cast, highsilicon-chromium steel valve seat insert which may have a carbon contentas high as 3.5% and which has metallurgical properties developed by asimplified heat treatment which omits heretofore required quenching anddrawing steps and still produces a hardness of from 35 to 45 Rockwell C.

ther and further objects of this invention Will be apparent to thoseskilled in the art from the following detailed description of theannexed sheet of drawings which, by way of an example only, illustratesa valve seat insert of this invention.

On the drawings:

Figure l is a fragmentary, vertical cross-sectional view, with parts inelevation, of the valve port area of an internal combustion engineequipped with a valve seat insert of this invention.

Figure 2 is an enlarged, fragmentary, vertical, crosssectional view ofthe valve seat insert area of the valve port of Figure l on an enlargedscale and illustrating the normal condition.

Figure 3 is a view similar to Figure 2 but illustrates the insert in acollapsed condition.

Figure 4 is a top plan view of the insert.

Figure 5 is a graphic reproduction of the microstructure of theheat-treated cast alloy for the insert.

As shown on the drawings:

In Figure 1 the engine valve port assembly 5 includes an engine block 6composed of cast iron, a cast valve seat insert 7 of the presentinvention press-fitted in an annular recess 8 of the block 6, a valvestem guide 9 press-fitted in a bore 10 of the engine block concentricwith the recess 8 and opening into the bottomof the recess, and a valve11 with the stem 11a thereof slidably mounted in the guide 9.

The valve seat insert 7 ha a cylindrical outer peripheral wall 7a, aflat bottom 7b, a flat top 7c, and a tapered seating face 7d convergingfrom the fiat top 70 to a cylindrical inner peripheral wall 72.

The recess 8 in the block 6 has a cylindrical side wall or shoulder 8aand a fiat bottom 8b.

The peripheralwall 70 has a snug fitting relation with the shoulder orwall 8a of the recess and the ring 7 is preferably press-fitted into therecess with the flat bottom of the insert seated on the flat bottom 8bof the recess.

The tapered seating face 7d of the insert mates with and receives thetapered seating face 11b of the valve head 11c.

In normal operation, the valve seat insert 7 will maintain its tight fitin the recess 8 as shown in Figure 2. Thus, the expansion of the ringand cylinder block are commensurate.

When the valve seat insert 7 is excessively heated to a point where itcan expand no further due to the re straining effect of the recess wall,it may become bowed asshown in Figure 3. This bowing may create a gapshown at 12 on an'exaggerated scale in Figure 3. If the insert 7 sets orcollapses in the condition shown in Figure 3, then the gap 12 will notbe reclaimed under lower operating temperatures. As a result, the insert7 will be loose in the recess 8. It will, therefore, be appreciated thatthe temperature at which the setting or collapsing of the insert takesplace, should be as high as possible to prevent looseness and permanentdistortion of the insert.

In accordance with this invention, the collapse" temperature of valveseat inserts is substantially increased by utilizing a cast valve seatinsert composed of a high silicon-chromium alloy of the followinggeneral composition:

Percent Carbon 0.7 to 3.5 Manganese 0.2 to 0.6 Nickel 1.0010 1:60Chromium 19.00to 21.00 Silicon 1.90 to 2.6 Iron Balance 'While the widecarbon range of the above general formula can be tolerated, it ispreferred to limit this range to about ;9% to 1.1%.

An alloy of the above composition is cast in suitable molds forproducingthe insert ring 7. Preferably, shell molds composed of thermoplasticresin-impregnated sand are usedalthough any known casting technique forpro ducing smooth accurate castings free from cracks, blowholes,shrinks, and the like, is acceptable.

The cast rings are heat-treated by an inexpensive twostep process forproducing the microstructure shown in Figure 5. The graphic illustrationin Figure represents the general nature -of the microstructure at 500magnification. As therein illustrated, crystals 12 are separated bygrain boundaries 14. The annealed structure is an aggregate ofunresolved carbides designated at 15 and the structure is generallycementitic. The general pattern is uniform and fairly free frommartensite. This microstructure is materially different from thehardened and drawn structure of the prior known forged inserts whichconsisted of an aggregate of carbides with martensite oriented in aninterdendritic pattern and with carbides definitely included in'thegrain boundaries and scattered throughout the matrix. The boundaries andthe matrix structure of the ring 7, however, are generally cementiticand relatively free from resolved carbides.

To produce the microstructure of Figure 5, the cast insert rings aresubjected to a two-step heat treatment. The first step includes heatingat temperatures from about 1500 to 1600 F., for about 1 hour. Thepreferred heating for this step is 1575 F. The heated rings are thenslowly cooled to a range of from about 1250 to 1350 F. This temperaturerange is maintained for about 1 hour. Preferably, a temperature of 1300F. is used. Heating is preferably carried out in an oven and the entireoven cycle period is about 6 to 6% hours. It is important, however, thatthe rings be held at the above indicated temperatures for a period ofabout 1 hour. The cooling rate from 1575 to 1300 F. should then be about4 hours.

If desired, the heated rings, after being maintained at temperaturesbetween 1500 to 1600 F. for about 1 hour, can be air-cooled to roomtemperature and can then be re-heated to 1250 to 1350 F. for about 1hour and air-cooled to room temperature. This modified heat treatment isadvantageous in permitting a staggering of the heat-treating steps.

By means of the simple two-step heat treatment procedures of thisinvention, the cast high silicon-chromium steel inserts will have aRockwell hardness of from 28 to 45 C and a collapse temperature of fromabout 1000 to 1l000 F.

A convenient collapse test for the rings is accomplished by inserting aring in a cast iron cup receiving a high-frequency induction coil intothe hollow interior of the ring. A water ring surrounds the cast ironcup. The insert is then intermediately heated by the induction coil andcooled by water spray on the cast cup. The insert is heated first to 300F. for several hundred cycles. It is then cooled and checked forlooseness. The temperature is then increased in -degree increments andthen cycled heating is repeated for several hundred cycles. Theprocedures continue until the insert, under test, loosens in the castiron cup. The final temperature is then recorded as the looseningtemperature or collapse temperature. The test is made to approximateengine conditions in the field.

From the above descriptions it will be understood that this inventionnow provides a cast va e 565i insert for Percent Carbon 0.9 to 1.1Manganese 0.2 to 0.6 Nickel 1.00 to 1.60 Chromium 19.00 to 21.00 Silicon1.90 to 2.6 Iron Balance said ring having a cementitic microstructurecomprising substantially a uniform aggregation of unresolved carbidesdeveloped by a two-stage heat treatment at temperatures of from about1500 to 1600 F. for about 1 hour followed by temperatures 'of about 1250to 1350 F. for about 1 hour.

.2. The method of increasing the collapse resistance of cast iron valveseat insert rings which comprises heating toa temperature of about 1500to 1600 F. for about 1 hour a cast'chromium steel alloy ring of thefollowing analysis:

Percent Carbon 0.9 to 3.5 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60Chromium 19.00 to 21.00 Silicon 1.90 to 2.6 Iron Balance slowly coolingsaid ring, heating the cooled ring for about 1 hour to temperaturesbetween about 1250 to 1350" F. and thereafter air-cooling the ring toproduce a cementitic iron structure.

'3. A cast silicon-chromium steel alloy of the following formula:

Percent Carbon 0.9 to 3.5 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60Chromium 19.00 to 21.00 Silicon 1.90 to 2.6 Iron Balance said alloyhaving a Rockwell hardness of from about 28 to 45 C, and-a collapsetemperature 'of from about 1000 to 1100 F., said alloy comprisingsubstantially a uniform aggregation of carbides unresolved; thestructure being cementitic.

4. A cast high temperature resisting iron valve seat insert for internalcombustion engines comprising a ring having the following formula:

Percent Carbon 0.9 to 3.5 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60Chromium 19.00 to 21.00 Silicon 1.90 to 2.6 Iron Balance said ringhaving a cementitic microstructure comprising substantially a uniformaggregation of unresolved carbides developed by a two-stage heattreatment at temperatures offrom about 1500 to 1600 F. for about 1 hourfollowed by temperatures of about 1250 to 1350 F. for about 1 hour.

5. In a method for producinga valve seat insert ring having a collapseresistance in excess of 1000 F., the

stepscomprising: casting a valve seat insert ring from a chromium steelalloy having the following formula:

Percent Carbon 0.9 to 1.1 Manganese 0.2 to 0.6 Nickel 1.00 to 1.60Chromium 19. 00 to 21.00 Silicon 1.90 to 2.6

Iron Balance heating the resulting cast ring to a temperature range of"from about 1500" to 1600" F. for about 1 hour; cooling said ring to atemperature range of from about 1250 to 1350 F.; and maintaining saidring at said last mentioned temperature range for about 1 hour toproduce a cast valve seat insert ring having a cementitic microstructurecomprising a substantially uniform aggregation of unresolved carbidesand having a Rockwell hardness of from about 28 to 45 C.

Stainless Iron and Steel, vol. I, Stainless Steel in Industry, pages 38and 39.. Edited by Monypenny. Published in 1951 by Chapman and HallLimited, London.

1. A CAST HIGH TEMPERATURE-RESISTING IRON VALVE SEAT INSERT FOR INTERNALCOMBUSTION ENGINES COMPRISING A RING HAVING THE FOLLOWING FORMULA: